Overvoltage surge protectors are used in many electrical and electronic circuitry. For example, it is well known that the semiconductor junctions that make up the solid state devices used in discrete transistor and integrated circuits are very sensitive to overvoltages. A voltage spike of even transient duration can destroy a given junction and render the electronic equipment of which it is part inoperable. Typically, these voltage spikes represent a high amplitude, short duration overvoltage pulse, or, sometimes, ringwave. The form or type of pulse depends on such things as cause of transient, impedance of the line, and load impedance.
Electrical surges or transients are inevitable. Typically, they are created by lightning, electric utility switching operations, and the cycling on and off of large inductive loads. Rural locations have more direct exposure to lightning. Metropolitan areas are more likely to experience switching transients. Factories are also subjected to internally generated transients created by the starting and stopping of electrical machinery such as arc welders and punch presses. In office buildings, copy machines or elevators may be principal surge producers.
The responsibility rests with the user to install transient overvoltage protection which will attenuate power line disturbances to a safe nondestructive level which matches the voltage tolerances of the equipment protected.
After documenting surges on AC power circuits, engineers arrived at an industry consensus on a practical guide for describing surge voltages on AC power circuits rated up to 600 volts. The resulting IEEE Std. 587-1980 has become American National Standard ANSI/IEEE C62.41-1980. This is the principal reference for surge current and surge voltage waveforms and amplitudes when evaluating transient voltage suppressors. The reference lists three standard waveforms, two of which are impulse and ringwave, and three location categories, two of which are service entrance and panelboard.
Generally, the objective is to clip the transient as quickly as possible by providing a low impedance path for same at a defined voltage level. The more inductance there is between the actual protective device (MOV or zener diode) and the line being clamped or protected, the less effective is the spike arresting action. The actual clamping voltage of the protective device can be stated as follows:
Clamping Voltage=MOV voltage+the IR drop of the wiring+LdI/dT where PA1 L=inductance PA1 I=current PA1 T=time PA1 R=resistance
Hence it is desirable to reduce the inductance to as low a level as possible and thereby increase the effectiveness of the protective device. Normal runs of wire, either independently connected or on conventional circuit boards, have considerable self-inductance, and this leads to reduced effectiveness of the spike arrester.
It is the object of the present invention to provide improved surge protectors and transient overvoltage arresters, overcoming the disadvantages and difficulties of the prior art devices.
It is another object to provide an improved circuit board having minimal inductance for use in electrical and/or electronic devices such as surge protectors.
Other objects and features of the present invention will become apparent from the following detailed disclosure considered in connection with the accompanying drawings.